2007 Annual Report 1a.Objectives (from AD-416) Identify mechanisms of heat tolerance at ambient and elevated CO2 among cultivars of soybean, dry bean, grain sorghum, and maize showing different pollen development, reproductive growth, yield, and seed quality sensitivities to heat stress. Determine if yield failures under high temperatures are mediated by low oxygen in reproductive tissues. Determine photosynthetic mechanisms of C4 plant responses to increased CO2, and to increased CO2 under elevated temperatures and/or water deficit. 1b.Approach (from AD-416) Selected soybean, sorghum, and maize cultivars will be grown at current doubled CO2 in Gainesville ambient and +4.5 Celsius sections of temperature-gradient greenhouses to identify heat tolerant cultivars. For grain sorghum and maize in sunlit controlled-environment chambers, procedures will be used to identify heat-sensitive points in pollen sugar transport and/or starch metabolism, and to identify genes that are sensitive to heat in the sucrose'starch pathway in developing pollen. Microprobes will be used to determine oxygen in soybean and dry bean pods and seeds as affected by temperature and ambient oxygen. Seeds produced from all studies will be analyzed for phytochemicals of interest for human nutrition. Measurements of leaf gas exchange, enzyme activities, and metabolic products will be used to test hypotheses that positive C4 plant response to high CO2 results from enhanced photosynthesis in early stages of leaf development. 3.Progress Report In collaboration with ARS in Phoenix, AZ the experimental phase of research on the evaluation of new Infrared Heaters for use in conducting temperature X CO2 studies in FACE experiments was completed in early FY2000. These studies were conducted in the Soil-Plant Atmosphere Research (SPAR) chambers in Gainesville. The data analysis phase has just begun. Other studies indicated that the aerodynamic resistance of peanut canopies within the SPAR chambers was small with respect to the ensemble leaf stomatal resistances. This finding indicates that data collected from SPAR chambers should be just as valid as data collected from free-air CO2 enrichment (FACE) studies. This is an important observation because of criticisms that outdoor, controlled-environment chambers do not represent “natural free-air-flow conditions.” Details on the success of the research on the impact of high temperature induced stresses on physiology, biochemistry, and gene expression aspects of pollen sterility of grain sorghum will be reported in another collaborating CRIS project of the Chemistry Research Unit. Likewise, progress on the impact of elevated temperature and CO2 on phytonutrients (tocopherols) in various cultivars of rice will be reported by the Phytonutrients Laboratory, Beltsville, Maryland. 4.Accomplishments Title: Quantifying crop seed yield decreases in response to elevated temperatures--soybean is generally less sensitive to higher temperatures than rice. Prior research showed that seed yields of all crop plants decrease with increasing temperature above the specific optimum temperature for each species and cultivar, which indicates that food production could adversely impacted by Global Warming. However, the range of sensitivity of seed yields among cultivars within crop species was not known. Therefore, over a six-year period, seed yield responses to a temperature increase of 4.5 degrees C (8.1 degrees F) above Gainesville, Florida ambient summertime temperatures were measured on forty-four cultivars of rice and forty-eight cultivars of soybean grown in field soil within temperature-gradient greenhouses. Cultivars of rice showed a greater range of sensitivity of seed yields to elevated temperature than cultivars of soybean. The greatest tolerance to high temperature in rice was exhibited by the cultivar N-22 from India. Most of the soybean cultivar seed yields were less sensitive to elevated temperatures than rice. Finally, these findings provide background information for rice and soybean plant breeders for improving crop seed yield tolerance to higher temperatures that are predicted due to global warming. This information also provides a cultivar comparison basis for molecular geneticists to identify genetic and physiological reasons for plant tolerance (or sensitivity) to high temperatures. Research addresses National Program 204, Global Change, Component III: Agricultural Ecosystems Impacts, Problem Statement 1: Cropping Systems. 6.Technology Transfer Number of non-peer reviewed presentations and proceedings 3 Review Publications Prasad, P.V.V., Boote, K.J., Allen Jr, L.H. 2006. Adverse high temperature effects on pollen viability, seed-set, seed yield and harvest index of grain-sorghum [Sorghum bicolor (L.) Moench] are more severe at elevated carbon dioxide due to higher tissue temperatures. Agricultural and Forest Meteorology. 139:237-251. Valero-Arcama, C., Kane, M., Wilson, S., Vu, J.C., Anderson, J.C., Philman, N. 2006. Photosynthetic and carbohydrate status of easy and difficult-to-acclimate sea oats (Uniola Paniculata L.) genotypes during in vitro culture and ex vitro acclimation. In Vitro Cellular and Developmental Biology - Plants. 42:572-583. Vu, J.C., Allen Jr, L.H., Widodo, W. 2007. Leaf photosynthesis and Rubisco activity and kinetics of soybean, peanut, and rice grown under elevated atmospheric CO2, supraoptimal air temperature, and soil water deficit.Current Topics in Plant Biology. 7:27-41.